1. Field of the Invention
The present invention relates to a thin plate member with a concave for mounting a semiconductor chip to form a semiconductor package which is excellent in manufacturing easiness, size precision and heat radiation property, and a method for manufacturing the thin plate member.
2. Description of the Prior Art
In the field of semiconductor packages, there have been various kinds of parts of semiconductor packages. The parts of semiconductor packages are made of various materials and various structures have been proposed, depending on the specifications of mounting chips and applications of these parts, such as those disclosed in, for example, Japanese Patent Application Laid-open Publication No. 60-226148 and Japanese Patent Application Laid-open Publication No. 2-106055. A few typical structures of semiconductor packages are shown in FIGS. 1 to 5.
FIG. 1 shows a pin-grid-array (PGA) type package, in which a substrate 1 and a cap 2 form a container, and a semiconductor chip c is mounted on a recess of the substrate 1 by fixing it with a bond b. A reference numeral 3 denotes a bonding wire. FIG. 2 shows a case where a resin 4 is charged into the container which is formed by the substrate 1 and the cap 2.
FIG. 3 shows a ball-grid-array (BGA) type package. In this package, the chip c mounted on a recess of the substrate 1 is sealed by a resin 4, and a resin substrate 5 is loaded on the substrate 1. Moreover, a solder mask 6 being connected with bonding wires 3 to the chip c and solder balls 7 are provided on the substrate 5. FIG. 4 shows a tape-ball-grid-array (T-BGA) type package, which is a modification of the BGA type package, where the solder mask 6 and the solder balls 7 are provided on a base film 5a in place of the resin substrate 5. The substrate 1 of this package has almost a uniform thickness at its every portion and it is formed into a convex shape in accordance with the shape of the recess in which the chip c is mounted, so as to protrude toward the outside (downward in the drawing). This substrate also works as a heat spreader.
FIG. 5 shows another package in which the substrate 1 and the cap 2 forms the container for accomodating the chip c in the manner similar to that shown in FIG. 1. However, in this case, a venthole 2a is provided on the cap 2. The chip c is arranged in the container with a lead frame paddle 8, and a lead frame 9 to be connected to the bonding wire 3 is provided at the connection between the substrate 1 and the cap 2.
The substrate 1 and the cap 2 for forming the package as described above are often made of aluminum or aluminum alloy with good heat radiation and small specific gravity, and they are shaped as a thin plate-like member with such a material so as to have a thickness of around 1 mm. This plate-like member is manufactured by blanking a thin molten plate material of a uniform thickness and shaping it by plastic deformation such as drawing or stamping (which is disclosed, for example, in Japanese Patent Application Publication No. 6-53297). For the aluminum alloy, specifically, an alloy having a composition of 2.2 to 2.8% of magnesium, 0.15 to 0.35% of chromium and the balance aluminum which is regulated in the Japanese Industrial Standard (JIS) No. A5052, and an alloy of JIS No. A6061 having a composition of 0.8 to 1.2% of magnesium, 0.4 to 0.8% of silicon, 0.15 to 0.4% of chromium and the balance aluminum have been employed.
As other materials, copper and copper alloy with better thermal conductivity have been also used, though with higher specific gravity than that of an aluminum alloy. This copper alloy is a molten material having a composition of 2 to 12% of aluminum and the balance copper, or of 3% of aluminum, 2% of silicon and the balance copper, or the like. The plate-like member made of these are manufactured in a similar manner to that as explained for the aluminum alloy.
It is necessary for these metal plate-like members for a semiconductor package to have strength sufficient for protecting the chip c, a thin and compact shape with light weight, and satisfactory heat radiation. In addition, it is also important to have satisfactory size precision with no thermal deformation, because if deformation or twist occurs by a heat cycle at the time of solder reflow, this causes an unsatisfactory bonding or pealing. The conventional parts as described above do not meet these requirement on performance satisfactorily. Therefore, a further improvement in performance in view of material properties and the like has been desired.
If the recess for accommodating the chip and the venthole 2a are formed by drawing or coining a thin plate material according to the conventional method, there is a problem that a wave-shaped wrinkle may be formed at the corner of the recess or that a crack arises near the corner. Moreover, there is a problem that an internal stress increases at the time of solder reflow due to an internal distortion generated by plastic deformation, which leads to an easy occurrence of thermal deformation.
These problems can be solved to some extent if a stress releasing process is added, or if the clearance of the processing mold for drawing process is improved or if there is provided some meansures for subjecting the thin plate material to a heat treatment for making it soft in advance. However, these measures not only bring about an increase in the processing costs but also make it difficult to manufacture the substrate 1 of the T-BGA type to form it into the intended shape. There is also a method for manufacturing the thin plate member having a recess by superimposing a flat and thin plate member on a ring-shaped thin plate member (the latter being called a support ring) and joining them together. However, this method has a problem in that the manufacturing cost is raised since a bonding agent and a connecting process are necessary, and that it is not possible to maintain the flatness of the thin plate part with high precision.